4.1.2 - alkanes

• An alkane is a saturated hydrocarbon containing only C-H bonds
• The general formula of an alkane is CnH2n+2
• Alkanes bonds are non-polar because carbon and hydrogen have similar electronegativities
• Alkanes shape is tetrahedral with a bond angle of 109.5 degrees
• Alkanes have london forces (intermolecular forces) because the bonds are non-polar
• As alkane chain length increases the boiling point increases because there is more surface area and contact points so more London forces. Therefore more energy is required to overcome the attraction.
• Branched molecules have lower boiling points to their equivalent straight chain because they have fewer contact points and therefore less london forces.
• Alkanes are insoluble in water because hydrogen bonds in water are stronger than alkanes london forces of attraction.
• Alkanes are very unreactive because they’re saturated.
• Combustion is an oxidation reaction.
• Complete combustion is combustion that occurs in a plentiful supply of oxygen (air)
• The Bunsen burner flame is blue during complete combustion
• Incomplete combustion of alkanes is combustion in a limited supply of oxygen

  its products are water, carbon dioxide and carbon monoxide
• The equation for the complete combustion of propane is:

  C3H8 + 5O2 —> 3CO2 + 4H2O
• Longer chain hydrocarbons are most likely to undergo incomplete combustion
• Soot (carbon) causes asthma, cancer and global dimming as an environmental impact
• Halogenoalkanes are formed from alkanes by free radical substitution
• In the presence of UV light alkanes react with halogens
• Propagation is the chain part of the reaction where products are formed but free radicals remain.
• Termination is when free radicals are removed by forming stable products
• The overall reaction for the free radical substitution of CH4 with Cl2 is

  CH4 + Cl2 —> CH3Cl + HCl
• The sigma bond in alkanes is a covalent bond which has a direct overlap of the electron clouds of the bonding atoms